1. Field of the Invention
The invention relates to devices for preparing and terminating optical fibers for interconnection in telecommunications networks using plug and socket assemblies that align the optical fibers for optimal signal transmission without the use of ferrules. More particularly, the present invention facilitates field processing of one or more cleaved and polished bare fiber ends using an apparatus for temporary containment during suitable preparation of terminal portions of optical fiber cables for field installation into the plug portion of an optical fiber plug and receptacle connector.
2. Description of the Related Art
The use of optical fibers in telecommunications networks offers the advantage of broader bandwidth when compared to the copper wire systems that have dominated this industry. Today""s high speed, bandwidth-intensive computing environments provide justification for increased use of optical fiber cables. The demand for optical fiber is expected to increase as transmission protocols reach higher and higher speeds and bandwidth requirements continue to grow. Until recently, cost was a deterrent to the use of optical fiber systems. The impact of cost has become less severe because of improvement in the supporting electronics and optical communications infrastructure. In addition, an increase in the volume of optical fiber production has driven down the cost of optical fiber components and devices. Optical fiber systems will become the preferred choice as component and installation costs approach parity with copper wire systems.
As with copper wire, it is necessary to provide means for interconnection and termination of optical fibers. Interconnection of optical fibers may be achieved by a number of methods including the methods of splicing and connecting. A splice is generally understood to be the formation of a permanent connection between a pair of optical fibers. The act of connecting optical fibers requires a device, i.e. a connector that facilitates repeated engagement and disengagement of optical fibers. An optical fiber connector, for one or more optical fibers, typically includes a plug portion and a receptacle or socket portion. Insertion of the plug portion into the receptacle portion provides interconnection for optical signal transmission between optical fibers. During the mating of a plug portion with a receptacle portion of an optical fiber connector, there is the need to provide accurate axial alignment of lengths of optical fiber for the number of optical fibers contained within each plug or receptacle. One requirement of an optical fiber connector is the joining together of lengths of optical fibers so aligned that light energy will propagate from one fiber to the other without insertion loss that may be observed as an appreciable light attenuation. To reduce insertion loss at the point of optical fiber connection, it is necessary to have precise registration and abutting fiber contact across the entire end of each optical fiber end face.
A broad range of devices exist for connecting and aligning optical fibers, whether the connection includes only a pair of optical fibers, i.e. one optical fiber in both the plug and receptacle portion of the optical fiber connector, or two or more fiber pairs. The majority of connectors include ferrules that rely on alignment of the outer surface of each ferrule to provide fiber alignment during termination, polishing and a positioning of each optical fiber end in an optical fiber connector.
A relatively recent development in optical fiber interconnection devices eliminates the need for ferrule-terminated optical fibers. These alternate plug and socket connectors use fiber guiding V-grooves to align cleaved and polished end portions of stripped optical fibers for optimum signal transmission. Connector assemblies using V-grooves for optical fiber alignment are adaptable to the needs of simplex (one fiber), duplex (two fibers), and multiplex (two or more fibers) connectors. They also offer advantages over ferrule-terminated optical fibers such as fewer component parts, smaller size and convenient assembly.
Further discussion emphasizes connector assemblies using V-groove alignment of optical fibers that undergo repeated engagement and disengagement. U.S. Pat. No. 5,381,498 describes a modular, multi-fiber connector comprising a plug and receptacle having an appearance similar to a conventional RJ 45 jack for copper conductors. The plug includes a body having a surface with several grooves that position and limit movement of otherwise free end portions of optical fibers. Fibers inside the receptacle are free to move into the grooves inside the plug body and into forcible abutment with the terminal ends of the plug fibers during insertion of the plug through an opening in the body of the receptacle. U.S. Pat. Nos. 5,757,997 and 6,026,210 and related patents, for example, describe subsequent development of connectors using V-groove alignment of optical fibers. These later versions of optical fiber connectors include features such as internal fiber splices using crimp elements, similar to those described in U.S. Pat. No. 5,638,477, and optical fiber holders of the type described in U.S. Pat. No. 6,078,719. Optical fiber holders become permanently applied around one or more optical fibers during fiber preparation using a device that cleaves stripped terminal portions of one or more optical fibers to a length determined by the dimensions of the optical fiber receptacle. The cleaving process has the capability for precise cleaving and polishing to produce multiple optical fibers having substantially the same length. U.S. Pat. Nos. 5,813,902, and 6,099,392 further describe systems and processes for cleaving and polishing terminal portions of optical fibers prior to assembly of connector receptacles or sockets in the field.
Implementation of optical fiber cable networks using cable interconnection based upon V-groove connectors requires field termination for either a connector receptacle or a connector plug or both. Field installation of optical fiber cables employs known methods for applying a receptacle or socket to a stripped end portion of one or more optical fibers. The lack of a corresponding method for field installation of connector plugs limits field-termination capability to optical fiber cables having a connector receptacle at each end. This limitation restricts optical fiber cable interconnection to a single option in which field-terminated cables, having connector receptacles at both ends, alternate with factory terminated cables, having connector plugs on both ends. Factory production of connector plug terminated optical fiber cables typically provides a limited variety of standard cable lengths. The use of pre-terminated standard lengths of optical fiber cable prevents the use of normal methods for installing optical fiber cable by pulling it through cable ducts or the like before applying connector plugs and sockets for interconnecting lengths of cable. Pre-terminated, factory assembled, optical fiber cables add expense and require more cable duct space than conventional cable systems. Reliance on standard lengths of terminated cables also denies the advantage of efficient use of space associated with custom installations. To provide more options and to facilitate installation of custom cable networks, there is a need for field installable optical fiber connector plugs so that cable network installers may choose whether to terminate a particular cable with either a connector plug or a connector socket.
The present invention provides an apparatus used during cleaving and polishing of optical fibers to be inserted into a connector plug body that accommodates one or more optical fibers. Connector plugs according to the present invention include several different embodiments having design features that facilitate preparation and insertion and splicing of optical fibers by a person who is relatively unskilled as an assembler of optical fiber connector components. Optical fiber insertion may be done by hand as a field operation requiring only the use of a crimp tool, for crimp element closure, to secure and retain one or more spliced optical fibers inside a connector plug.
Field installation of optical fiber connector plugs, in conjunction with the previously discussed field installable receptacles, offers several benefits including convenience, development of custom network segments, and the opportunity to order bulk supplies, rather than an array of standard components. These benefits could contribute to a reduction of optical fiber cable network installation costs.
The use of connector plugs and processes according to the present invention with previously available field installable sockets is convenient because it moves optical fiber termination from the controlled assembly environment of the factory to the field location where actual installation requirements are more clearly seen. Given the opportunity to construct cable systems to match the needs of a particular installation, an assembler is no longer limited to using factory terminated, standard cable lengths but has the advantage of custom building interconnecting cables. Custom interconnecting cables may be prepared using bulk optical fiber cable and connector components that may prove to be a less expensive option than reliance on supplier-determined, standard lengths of plug terminated cables. Field termination of connector plugs allows cable installers to return to more conventional methods of network installation.
The present invention includes an article used in the process of cleaving and polishing the ends of optical fibers before termination inside a connector plug or socket of an optical fiber connector assembly. An optical fiber connector assembly includes a connector plug and socket having V-grooves, rather than ferrules, for aligning cleaved and polished ends of terminal portions of optical signal-carrying optical fibers.
Articles for preparing optical fibers for termination are referred to herein as xe2x80x9cpucksxe2x80x9d for cleaving and polishing optical fiber ends. Initial preparation of a cable, containing one or more individual optical fibers, requires that the sheath and buffer layers be stripped from a generous terminal portion of each optical fiber.
A puck, as described herein, has a design with enough room to accommodate a single optical fiber or multiple fibers simultaneously during the process of optical fiber cleaving and polishing. Simultaneous processing of multiple fibers produces cleaved and polished optical fiber ends on stripped terminal fiber portions of equal and precisely controlled length. The length requirements match those needed for optimum fiber positioning after insertion into the body of any of the embodiments of optical fiber connector plugs according to the present invention.
The process of cleaving and polishing the ends of optical fibers includes temporary insertion of stripped optical fiber terminal portions into a fiber holder that includes a spring clamp. Preparation for cleaving of optical fiber ends requires placement of the fiber holder in a recess in the puck so that short lengths of one or more optical fibers extend from the holder to pass through openings in a guide plate opposite a holder entry port that receives a portion of un-stripped optical fiber cable. Correct positioning of the holder in the recess places the jacketed cable, exiting the holder entry port, in a groove in the puck. A hinged lid, attached to the puck, closes over the holder and the jacketed optical fiber cable to grip the cable and actuate the spring clamp in the holder. A latching mechanism secures the hinged lid to the body of the puck preventing movement of either the un-stripped, jacketed cable or the stripped optical fiber terminal portions during cleaving of optical fiber ends. After loading and securing the holder and the optical fiber cable in the puck, cleaving of immobilized optical fibers produces optical fiber terminal portions of precise and equal length based upon the design and dimensions of the puck. The guide plate has a shape for mating in a required, fixed orientation with a groove in a cleaving and polishing device. After correct positioning of the puck, using the guide plate, stripped optical fibers, extending from the guide plate, are essentially perpendicular to a cleaving blade of the cleaving and polishing device. Smooth movement of the puck past the cleaving blade produces one or more cleaved optical fibers that optionally have slightly angled end faces at an angle of 10xc2x0 or less. Slightly angled and polished optical fiber end faces have been shown to provide optical splices that transmit optical signals with less signal attenuation than optical splices in which the polished end faces are substantially perpendicular to the longitudinal axis of the optical fiber.
The puck may be removed from the cleaving section of the cleaving and polishing device and, while still in the puck, and with the lid in its latched position, the cleaved optical fiber ends may be polished against a polishing strip using several repetitions of a rubbing motion. Cleaning of the fiber ends, after polishing, may be required, using conventional cleaning materials and methods, including liquid spray cleaning, to remove accumulated debris that could obscure the fiber end face causing optical signal attenuation. Thereafter, pivoting the guide plate, unlatching the hinged lid, lifting the jacketed cable and fiber holder, and separating the two main parts of the temporary holder releases the stripped, cleaved and polished optical fibers from the puck.
Field assembly of a connector plug involves the relatively simple process of inserting one or more optical fibers into one side of crimp elements. The crimp elements have limited movement in elongate depressions formed in the floor of the molded base of any one of several embodiments of connector plugs according to the present invention. Connector plugs may be used with single optical fibers, but preferably the plug has a design to accommodate two or more optical fibers. Most preferably the plug may be used as a duplex plug, for two optical fibers contained in a single-jacketed cable. Each optical fiber enters its assigned crimp element to the point at which it contacts the cleaved and polished face of an optical fiber stub that was factory installed at the opposite end of the crimp element. A crimp element has a size and internal design to provide accurate alignment, orientation and facial contact between each newly cleaved optical fiber end and each optical fiber stub. Interfacial contact for optimum signal transmission through multi-fiber connector plugs relies upon the equal length of the optical fiber terminal portions, having slightly angled, cleaved and polished end faces, and the precise positioning of the crimp elements within the connector plug. After achieving the desired positioning and alignment, the newly cleaved fiber ends may be secured in the crimp elements using a crimping tool, also referred to herein as a compression cap.
Optical signal transmission relies upon accurate alignment full surface contact of the slightly angled ends of optical fibers and optical fiber stubs spliced together using crimp elements as described previously. Other features of connector plugs according to the present invention facilitate insertion of one or more optical fibers into the body of a connector plug and allow component size reduction, which results in optical fiber cable installations requiring less space or containing increased numbers of plug and socket connections.
More particularly the present invention provides an article for temporarily retaining an optical fiber cable including a stripped terminal portion of at least one optical fiber requiring cleaving followed by polishing of an end face thereof. The article comprises a housing having a recess for a demountable optical fiber holder. A demountable optical fiber holder includes a base-plate having at least a first fiber channel formed therein to receive the stripped portion of the at least one optical fiber. The base plate has a number of pockets. A cover plate for the demountable optical fiber holder includes a spring clamp, at least a first upper channel and a number of posts to mate with the pockets of the base-plate to assemble the demountable optical fiber holder. The article further includes a guide plate attached at the distal end of the housing to pivot between a first pivot position and a second pivot position. The guide plate has at least one opening for the stripped portion of the at least one optical fiber. A rotatable lid attached to the housing rotates between an open position and a closed position. The lid includes a latch and a pressure bar, with the latch engaging the housing to bias the pressure bar against the spring clamp to hold the optical fiber immobile between the spring clamp and at least the first fiber channel when the demountable holder resides in the recess. The article temporarily retains the optical fiber cable for cleaving and polishing the end face thereof when the lid is closed.
The present invention also provides an optical fiber connector plug for mating with an optical fiber receptacle to form an optical fiber connection. The optical fiber connector plug comprises a connecting portion comprising a containment body including a rear entry at a first end and a first fiber stub exit opening to a first fiber stub channel. The first fiber stub exit is parallel to a second fiber stub exit opening to a second fiber stub channel. The first and second fiber stub exits are formed at a second end opposite the first end of the containment body. The rear entry divides at a junction into a first fiber groove and a second fiber groove that diverges from the first fiber groove. The containment body includes first and second crimp elements each having an open-ended bore coaxial with the first and second fiber grooves. Each crimp element contains a optical fiber stub. A molded top attached to the containment body includes a substantially rectangular opening. The opening contains a compression element that moves between a first position and a second position to apply force to the first crimp element and the second crimp element. In its first and second positions the compression element first adjusts each bore and then forms splices by capturing a stripped, cleaved and polished end portion of an optical fiber and an optical fiber stub in each of the crimp elements. A bend relief boot encloses the connecting portion at one end, while a shroud releasably engages it at the other end.
The present invention further provides an optical fiber connector plug for mating with an optical fiber receptacle to form an optical fiber connection. The optical fiber connector plug comprises a connecting portion comprising a containment body including a rear entry at a first end and a first fiber stub exit opening to a first fiber stub channel. The first fiber stub exit is parallel to a second fiber stub exit opening to a second fiber stub channel. The first and second fiber stub exits are formed at a second end opposite the first end of the containment body. An optical fiber connector plug according to the present invention includes a holder for permanent retention of at least one stripped, cleaved and polished end portion of a an optical fiber. The holder has a size for insertion into the rear entry of the containment body. The containment body includes first and second crimp elements each having an open-ended bore coaxial with the fiber stub channels. Each crimp element contains a optical fiber stub. A molded top attached to the containment body includes a substantially rectangular opening. The opening contains a compression element that moves between a first position and a second position to apply force to the first crimp element and the second crimp element. In its first and second positions the compression element first adjusts each bore and then forms splices by capturing a stripped, cleaved and polished end portion of an optical fiber and an optical fiber stub in each of the crimp elements. A bend relief boot encloses the connecting portion at one end, while a shroud releasably engages it at the other end.
According to the present invention a process may be used for field terminating at least one optical fiber in an optical fiber connector plug. The process comprises a number of steps including providing an article for retaining an optical fiber cable. The article comprises a housing having a recess for an optical fiber holder. The article further includes a guide plate attached at the end of the housing to pivot between a first pivot position and a second pivot position. The guide plate has at least one opening for a stripped portion of at least one optical fiber. A rotatable lid attached to the housing rotates between an open position and a closed position. The article temporarily retains the optical fiber cable for cleaving and polishing the end face of the optical fiber when the lid is closed. The guide plate engages a cleaving device for cleaving at least one optical fiber. This is followed by polishing the end face of the at least one cleaved fiber end to provide a stripped, cleaved and polished end portion of at least one optical fiber. Removal of the optical fiber cable and the demountable optical fiber holder from the article precedes release of the stripped, cleaved and polished end portion of the at least one optical fiber from the optical fiber holder. The optical cable is then terminated by inserting the stripped, cleaved and polished end portion of at least one optical fiber into an optical fiber connector plug that has a connecting portion using crimp elements to splice the stripped, cleaved and polished end portions of optical fibers to optical fiber stubs located at the front of a connector plug. After completing splices, applying a bend relief boot to enclose one end of the connecting portion and engaging a shroud over the other end provides at least one optical fiber terminated by an optical fiber connector plug according to the present invention.